Math Problem Statement

find the solutions to z squared = 1-i square root of 3

Solution

To find the solutions to the equation z2=1i3z^2 = 1 - i\sqrt{3}, let's break it down step by step.

Step 1: Express the complex number in polar form

The given complex number is 1i31 - i\sqrt{3}. We need to express this in polar form, which is rcisθ=r(cosθ+isinθ)r \text{cis} \theta = r(\cos \theta + i \sin \theta), where rr is the modulus and θ\theta is the argument.

  1. Modulus rr: r=(1)2+(3)2=1+3=4=2r = \sqrt{(1)^2 + (-\sqrt{3})^2} = \sqrt{1 + 3} = \sqrt{4} = 2

  2. Argument θ\theta: The argument θ\theta is the angle the complex number makes with the positive real axis. Since the complex number is 1i31 - i\sqrt{3}, it lies in the fourth quadrant.

    θ=tan1(31)=π3\theta = \tan^{-1}\left(\frac{-\sqrt{3}}{1}\right) = -\frac{\pi}{3}

So, in polar form, 1i3=2cis(π3)1 - i\sqrt{3} = 2 \text{cis}\left(-\frac{\pi}{3}\right).

Step 2: Use De Moivre's Theorem

We know that z2=rcisθz^2 = r \text{cis} \theta, and we are trying to find zz. So, to solve for zz, we need to take the square root of both sides.

Let z=r1/2cis(θ+2kπ2)z = r^{1/2} \text{cis} \left(\frac{\theta + 2k\pi}{2}\right), where k=0,1k = 0, 1 gives the two distinct solutions.

  1. Modulus: 2=r\sqrt{2} = \sqrt{r}

  2. Arguments: For k=0k = 0: θ1=π3+2(0)π2=π6\theta_1 = \frac{-\frac{\pi}{3} + 2(0)\pi}{2} = -\frac{\pi}{6}

    For k=1k = 1: θ2=π3+2(1)π2=5π6\theta_2 = \frac{-\frac{\pi}{3} + 2(1)\pi}{2} = \frac{5\pi}{6}

Step 3: Write the solutions

The two solutions are:

  1. z1=2cis(π6)=2(cos(π6)+isin(π6))z_1 = \sqrt{2} \text{cis} \left(-\frac{\pi}{6}\right) = \sqrt{2} \left( \cos \left(-\frac{\pi}{6}\right) + i \sin \left(-\frac{\pi}{6}\right) \right) z1=2(32i12)=62i22z_1 = \sqrt{2} \left( \frac{\sqrt{3}}{2} - i \frac{1}{2} \right) = \frac{\sqrt{6}}{2} - i \frac{\sqrt{2}}{2}

  2. z2=2cis(5π6)=2(cos(5π6)+isin(5π6))z_2 = \sqrt{2} \text{cis} \left(\frac{5\pi}{6}\right) = \sqrt{2} \left( \cos \left(\frac{5\pi}{6}\right) + i \sin \left(\frac{5\pi}{6}\right) \right) z2=2(32+i12)=62+i22z_2 = \sqrt{2} \left( -\frac{\sqrt{3}}{2} + i \frac{1}{2} \right) = -\frac{\sqrt{6}}{2} + i \frac{\sqrt{2}}{2}

Final Solutions:

z1=62i22,z2=62+i22z_1 = \frac{\sqrt{6}}{2} - i \frac{\sqrt{2}}{2}, \quad z_2 = -\frac{\sqrt{6}}{2} + i \frac{\sqrt{2}}{2}

Would you like more details on any step or have questions?

Here are 5 related questions to expand on this topic:

  1. How do you convert any complex number into polar form?
  2. What is De Moivre’s theorem and how is it used for solving powers of complex numbers?
  3. What are the geometric interpretations of complex number solutions?
  4. Can this method be generalized for solving cubic equations with complex numbers?
  5. How do you solve equations involving higher powers of complex numbers?

Tip: Always check in which quadrant the complex number lies when finding the argument (angle), as it affects the sign of the trigonometric functions.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Polar Form
Roots of Complex Numbers

Formulas

r = √(a^2 + b^2)
θ = tan^(-1)(b/a)
z = r^(1/2) cis ((θ + 2kπ) / n) for k = 0, 1

Theorems

De Moivre's Theorem

Suitable Grade Level

Undergraduate (Math Major) or Advanced High School (Grades 11-12)